1. Field of the Art
The present embodiments relate to paper and paper making.
2. Description of Related Art
Paper is sheet material containing interconnected small, discrete fibers. The fibers are usually formed into a sheet on a fine screen from a dilute water suspension or slurry. Paper typically is made from cellulose fibers, although occasionally synthetic fibers are used. Paper products made from untreated cellulose fibers lose their strength rapidly when they become wet, i.e., they have very little wet strength. Wet strength resin can be added to the paper to produce stronger paper products. The types of wet strength resins that can be applied to paper may be either of the “permanent” or “temporary” type, which are defined, in part, by how long the paper retains its wet strength after immersion in water.
A common permanent wet strength resin is an epichlorohydrin-based wet strength resin, such as polyamidoamine epichlorohydrin (PAE). Conventional PAE resins can be prepared by reacting polyamidoamine with epichlorohydrin in the mole ratio of epichlorohydrin to secondary amine groups being from about 0.5 to 1 to about 1.8 to 1 (for example, as discussed in U.S. Pat. Nos. 2,926,116, 2,926,154, 5,171,795, 5,614,597, 5,017,642, 5,019,606, and 7,081,512, each of which is incorporated herein by reference). High permanent wet strength often leads to re-pulping issues during papermaking production. In addition, sanitary paper products with high permanent wet strength may clog sewage systems and/or septic tanks.
Glyoxalated polyacrylamide (GPAM) is a common temporary wet strength resin. GPAM is typically prepared by reacting glyoxal and a cationic polyacrylamide base polymer (for example, as discussed in U.S. Pat. Nos. 3,556,932, 4,605,702, 7,828,934, and US. Pat. Application Publication No. 2008/0308242, which are herein incorporated by reference). GPAM is typically added in the pulp suspension before paper sheet formation. Upon drying of the treated paper sheet, GPAM is believed to form covalent bonds with paper cellulose to increase paper dry strength. Since the covalent bond between GPAM and cellulose is reversible in water, this wet strength may decrease over time. GPAM strength performance also can be adversely affected by relatively high pH and high levels of alkalinity when present as bicarbonate ions.
The description herein of certain advantages and disadvantages of known methods and compositions is not intended to limit the scope of the present disclosure. Indeed the present embodiments may include some or all of the features described above without suffering from the same disadvantages.